Proxy Statement (Form DEF 14A)

Sixth Street Specialty Lending, Inc.

2100 McKinney Avenue, Suite 1500

Dallas, TX 75201

April 10, 2025

To Our Stockholders:

We are pleased to invite you to attend the 2025 Annual Meeting of Stockholders of Sixth Street Specialty Lending, Inc. to be held on May 22, 2025, at 9:30 a.m., EasteTime, at the offices of Simpson Thacher & Bartlett LLP, 425 Lexington Avenue, 30th Floor, New York, NY 10017.

The following pages include a formal notice of the meeting and our proxy statement. The Notice of Internet Availability of Proxy Materials that you received by mail and this proxy statement describe various matters on the agenda for the meeting. Please read these materials so that you will know what we plan to do at the meeting. It is important that your shares be represented at the annual meeting, regardless of whether you plan to attend the meeting in person. Please vote your shares as soon as possible through any of the voting options available to you as described in the Notice of Internet Availability of Proxy Materials and this proxy statement.

You will also receive separate proxy materials for a Special Meeting of Stockholders, which will be held at the same place and on the same date stated above, but not at the same time. Please be certain to use each proxy card that you receive from us to vote separately for the matters to be discussed at each meeting.

On behalf of management and our Board of Directors, we thank you for your continued support of Sixth Street Specialty Lending, Inc.

Important Notice Regarding the Availability of Proxy Material for the Annual Meeting of Stockholders to Be Held on May 22, 2025.

Our proxy statement and annual report on Form 10-Kfor the year ended December 31, 2024 are available online at www.proxyvote.com.

The following information applicable to the AnnualMeeting of Stockholders may be found in the proxy statement and accompanying proxy card:

Sixth Street Specialty Lending, Inc.

2100 McKinney Avenue, Suite 1500

Dallas, TX 75201

Notice of the 2025 Annual Meeting of Stockholders

TO OUR STOCKHOLDERS:

NOTICE IS HEREBY GIVEN that the 2025 Annual Meeting of Stockholders of Sixth Street Specialty Lending, Inc. will be held at the offices of Simpson Thacher & Bartlett LLP, 425 Lexington Avenue, 30th Floor, New York, NY 10017 on May 22, 2025, at 9:30 a.m., EasteTime. The 2025 Annual Meeting of Stockholders is being held for the following purposes:

1. To elect three Class II directors, each to serve for a three-year term and until a successor has been duly elected and qualified or until the director's earlier resignation or removal.

2. To ratify the selection of KPMG LLP as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2025.

3. To transact such other business as may properly come before the 2025 Annual Meeting of Stockholders or any postponement or adjournment thereof.

Only stockholders of record at the close of business on March 31, 2025, are entitled to notice of and to vote at the 2025 Annual Meeting of Stockholders or any postponement or adjournment thereof.

We are furnishing a proxy statement, annual report and proxy card to our stockholders on the internet, rather than mailing printed copies of those materials to each stockholder. If you received a Notice of Internet Availability of Proxy Materials by mail, you will not receive a printed copy of the proxy statement, annual report and proxy card unless you request them. Instead, the Notice of Internet Availability of Proxy Materials will instruct you as to how you may access and review the proxy statement and annual report, and vote your proxy, on the internet.

Your vote is extremely important to us. Whether or not you plan to attend the 2025 Annual Meeting of Stockholders, we encourage you to vote your proxy on the internet by following the instructions provided on the Notice of Internet Availability of Proxy Materials or proxy card. Stockholders may also request from us, free of charge, hard copies of the proxy statement and proxy card by following the instructions on the Notice of Internet Availability of Proxy Materials.

Further, from time to time, we may repurchase shares of our common stock and are notifying you of this ability as required by applicable securities law. See "Stock Repurchases" in the proxy statement.

April 10, 2025

YOUR VOTE IS IMPORTANT! WE HOPE YOU WILL VOTE OVER THE INTERNET, BY PHONE OR BY MARKING, SIGNING AND RETURNING YOUR PROXY CARD AS SOON AS POSSIBLE, WHETHER OR NOT YOU PLAN TO ATTEND THE MEETING. EVEN IF YOU VOTE YOUR SHARES PRIOR TO THE MEETING, YOU STILL MAY ATTEND THE MEETING AND VOTE YOUR SHARES IN PERSON.

TABLE OF CONTENTS

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Sixth Street Specialty Lending, Inc.

2100 McKinney Avenue, Suite 1500

Dallas, TX 75201

PROXY STATEMENT

FOR THE 2025

ANNUAL MEETING OF STOCKHOLDERS

The accompanying proxy is solicited on behalf of the Board of Directors (the "Board") of Sixth Street Specialty Lending, Inc., which is sometimes referred to in this proxy statement as "TSLX," "we," "us," "our," or the "Company," for use at the 2025 Annual Meeting of Stockholders (the "Meeting") to be held to be held at the offices of Simpson Thacher & Bartlett LLP, 425 Lexington Avenue, 30th Floor, New York, NY 10017 on May 22, 2025, at 9:30 a.m., EasteTime. Only holders of record of our common stock at the close of business on March 31, 2025, which is the record date, will be entitled to vote at the Meeting. At the close of business on the record date, we had 93,964,358 shares of common stock outstanding and entitled to vote.

It is anticipated that the Notice of Internet Availability of Proxy Materials will first be sent to Stockholders on or about April 10, 2025. This proxy statement, including the accompanying form of proxy card (collectively, the "Proxy Statement"), and the Company's Annual Report for the fiscal year ended December 31, 2024 will first be made available to stockholders on or about April 10, 2025. The Annual Report and Proxy Statement can both be accessed online at www.proxyvote.com.

All proxies will be voted in accordance with the instructions contained therein. Unless contrary instructions are specified, if the accompanying proxy is executed and returned (and not revoked) prior to the Meeting, the shares of the Company's common stock represented by the proxy will be voted (1) FOR the election of the Class II director candidates nominated by the Board and (2) FOR the ratification of the selection of KPMG LLP as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2025. Should any matter not described above be properly presented at the Meeting, the named proxies will vote in accordance with their judgment as permitted.

Voting Rights

Holders of our common stock are entitled to one vote for each share held as of the record date.

The 2025 Annual Meeting of Stockholders is being held for the following purposes:

1. To elect three Class II directors, each to serve for a three-year term and until a successor has been duly elected and qualified or until the director's earlier resignation or removal.

2. To ratify the selection of KPMG LLP as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2025.

3. To transact such other business as may properly come before the 2025 Annual Meeting of Stockholders or any postponement or adjournment thereof.

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Quorum, Effect of Abstentions and Broker Non-Votes,Vote Required to Approve the Proposals

A majority of the outstanding shares of common stock must be present or represented by proxy at the Meeting in order to have a quorum. If you have properly voted by proxy online, by phone, or via mail, you will be considered part of the quorum. We will count "abstain" and "withhold" votes as present for the purpose of establishing a quorum for the transaction of business at the Meeting. If at any time shares are held through brokers, we will count broker non-votesas present for the purpose of establishing a quorum. A broker non-voteoccurs when a broker holding shares for a beneficial owner votes on some matters on the proxy card, but not on others, because the broker does not have instructions from the beneficial owner or discretionary authority (or declines to exercise discretionary authority) with respect to those other matters.

Provided a quorum is present, directors are elected by a plurality of the votes represented at the meeting and voted for nominee(s) in the election. Broker non-votes,if any, though counted for purposes of establishing a quorum, will not affect the outcome of the voting on the elections. A proxy marked "withhold" with respect to a director nominee will result in such director nominee receiving one fewer "FOR" vote that would count towards a plurality.

The affirmative vote of the majority of shares represented at the meeting and voting on the proposal will determine the outcome of the ratification of the independent registered public accounting firm. For this proposal, "abstain" votes and broker non-votes,if any, though counted for purposes of establishing a quorum, will have no effect on the outcome of the vote.

The inspector of elections appointed for the Meeting will separately tabulate affirmative votes, "against" votes or "withhold" votes, as applicable, "abstain" votes and broker non-votes.

Adjournment of Meeting

In the event that a quorum shall fail to attend the Meeting, either in person or represented by proxy, the stockholders entitled to vote at the Meeting (present in person or represented by proxy) shall have the power to adjouthe meeting from time to time, without notice other than announcement at the meeting, until a quorum shall be present or represented by proxy. Any such adjournment proposed by a stockholder or person named as a proxy would require the affirmative vote of the majority of the outstanding shares present in person or represented by proxy at the Meeting. In addition, pursuant to the bylaws of the Company, if there are not sufficient votes for a quorum, the chairman of the Meeting, or any other officer entitled to preside or to act as secretary at the Meeting, may adjouor postpone the Meeting in order to permit further solicitation of proxies by the Company, without notice other than announcement at the meeting.

At any such adjourned or postponed meeting, any business may be transacted which might have been transacted at the meeting as originally called. If the adjournment is for more than 30 days, or if after adjournment a new record date is set, then a notice of the adjourned meeting shall be given to each stockholder of record entitled to vote at the meeting.

Proxies for the Meeting

The named proxies for the Meeting are Ian Simmonds and Anton Brett (or their duly authorized designees), who will follow submitted proxy voting instructions. They will vote as the Board recommends herein as to any submitted proxies that do not direct how to vote on any item, and will vote on any other matters properly presented at the Meeting in their judgment.

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Other Information Regarding This Proxy

The Company will pay the expenses of soliciting proxies to be voted at the Meeting. The Company has retained Broadridge Investor Communication Solutions, Inc. to assist with the distribution and collection of proxies for a fee of approximately $75,000, plus reimbursement of expenses.

In addition to the solicitation of proxies by the use of the internet, proxies may be solicited in person and/or by telephone, mail or electronic transmission by directors or officers of the Company and/or officers or employees of Sixth Street Specialty Lending Advisers, LLC, the Company's investment adviser (the "Adviser"). No additional compensation will be paid to such directors, officers or regular employees for such services. The address of the Adviser is 2100 McKinney Avenue, Suite 1500, Dallas, TX 75201.

Revocability of Proxies

A stockholder "of record" (i.e., stockholders holding shares directly in their name) may revoke any proxy by delivering a new proxy in accordance with applicable law, bearing a later date, by giving notice of revocation in writing to the Secretary of the Company prior to the Meeting or by attending the Meeting and voting in person. However, the mere presence of the stockholder at the Meeting does not revoke the proxy.

If your shares are held for your account by a broker, bank or other institution or nominee, you may vote such shares at the Meeting only if you obtain proper written authority from your institution or nominee and present it at the Meeting. If your shares are held for your account by a broker, bank or other institution or nominee, to revoke any voting instructions prior to the time the vote is taken at the Meeting, you must contact such broker, bank or other institution or nominee to determine how to revoke your vote in accordance with its policies with sufficient time in advance of the Meeting.

Contact Information for Proxy Solicitation

You can contact us by mail sent to the attention of the Secretary of the Company, Anton Brett, Sixth Street Specialty Lending, Inc., 888 7th Avenue, 41st Floor, New York, NY 10106, or by email at [email protected]. You can call us by dialing 469-621-2033.You can access our proxy materials online at www.proxyvote.com.

Attendance and Participation

The Meeting will be conducted in person at the offices of Simpson Thacher & Bartlett LLP, 425 Lexington Avenue, 30th Floor, New York, NY 10017. Stockholders as of the close of business on March 31, 2025, the record date, are entitled to participate in and vote at the Meeting. If you have a question pertaining to the business of the Meeting, please submit it in accordance with the procedures described below.

To participate in the Meeting, you will need the 16-digitcontrol number included on your proxy card, your voting instruction form, or the Notice of Internet Availability of Proxy Materials previously mailed or made available to stockholders entitled to vote at the Meeting.

In-personadmission to the Meeting will be on a first-come, first-served basis. Please bring proof of your common stock ownership, such as a current brokerage statement and photo identification. If you are representing an entity that is a stockholder, you must also present documentation showing your authority to attend and act on behalf of the entity (such as a power of attorney, written proxy to vote or letter of authorization on the entity's letterhead). We reserve the right to restrict admission to the meeting or limit the number of representatives for any entity that may be admitted to the meeting for security or health and safety reasons at our sole discretion.

The Annual Meeting of Stockholders will begin promptly at 9:30 a.m., EasteTime, and the Special Meeting of Stockholders will begin promptly at 10:00 a.m., EasteTime. Participants should allow plenty of time to check in prior to the start of the meetings.

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You can vote in person at the Meeting. If you hold your shares in "street name", you must obtain a proxy from the record holder to vote in person.

Street Name Holders

If your shares are held in a bank, brokerage or other institutional account, you are a beneficial owner of these shares but not the record holder. This is known as holding shares in "street name." If you wish to vote the shares you hold in "street name" in person at the meeting, you must obtain a legal proxy from your bank, broker or other intermediary and bring it with you to hand in with your ballot.

Stockholder List

The list of our stockholders of record entitled to vote at the Meeting will be made available for viewing by stockholders at the Meeting for any purpose germane to the Meeting.

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SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

Beneficial ownership is determined in accordance with the rules and regulations of the U.S. Securities and Exchange Commission (the "SEC"). These rules generally provide that a person is the beneficial owner of securities if the person has or shares the power to vote or direct the voting thereof, or to dispose or direct the disposition thereof or has the right to acquire these powers within 60 days. The following table sets forth, as of March 31, 2025, the beneficial ownership as indicated in the Company's books and records of each current director, the nominees for director, the Company's Named Executive Officers and the Company's executive officers and directors as a group. Based upon Schedule 13D or Schedule 13G filings with the SEC, the Company is not aware of any person that beneficially owns 5% or more of the outstanding shares of the Company's common stock.

The percentage ownership is based on 93,964,358 shares of common stock outstanding as of March 31, 2025. To the Company's knowledge, except as indicated in the footnotes to the table, each of the stockholders listed below has sole voting and/or investment power with respect to shares beneficially owned by such stockholder. Unless otherwise indicated by footnote, the address for each listed individual is 2100 McKinney Avenue, Suite 1500, Dallas, TX 75201.

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PROPOSAL NO. 1

ELECTION OF DIRECTORS

Our Board consists of ten members. The Board is divided into three classes, with the members of each class each serving staggered, three-year terms. The terms of our Class II directors will expire at the Meeting; the terms of our Class III directors will expire at the 2026 annual meeting of stockholders; and the terms of our Class I directors will expire at the 2027 annual meeting of stockholders.

The Board has nominated Judy Slotkin, P. Emery Covington and Jennifer Gordon, each to serve until their successor is duly elected and qualified at the annual meeting of stockholders held in 2028 or until their earlier death, resignation or removal. Mses. Slotkin, Covington and Gordon are currently directors of TSLX.

Mses. Slotkin, Covington and Gordon have consented to being named in this proxy statement and to serving as directors if elected at the Meeting. If, for any reason, any of them become unable or unwilling to serve at the time of the Meeting, the persons named as proxies in the proxy will have the authority to vote for a substitute nominee or nominees. We do not anticipate that Mses. Slotkin, Covington and Gordon will be unable or unwilling to serve.

The Board has determined that Mses. Slotkin and Covington are not "interested persons" of the Company, of the Adviser, or of any of their respective affiliates as defined in Section 2(a)(19) of the 1940 Act.

The Board recommends that stockholders vote "FOR" the Company's nominees for Class II Director.

Nominees for Election as Class II Director

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Biographical Information

Set forth below are brief biographies of Mses. Slotkin, Covington and Gordon and of all other members of the Board who will continue in office. On February 13, 2025, John Ross informed the Company of his intention to retire from the Board, effective as of the close of business on May 22, 2025. Accordingly, Mr. Ross will not run for re-electionto the Board at the Meeting. Also included below following each biography is a brief discussion of the specific experience, qualifications, attributes or skills that led our Board to conclude that the applicable director should serve on our Board at this time. In addition, set forth further below is a biography of each of our executive officers who is not a director.

Incumbent Class II Directors: Term Expiring 2025

Jennifer Gordon was elected a director of TSLX in January 2019. Ms. Gordon is a Vice President of TSLX and is a Partner and Chief Compliance Officer of Sixth Street. She also currently serves on the board of Sixth Street Lending Partners. Until Ms. Gordon's election to the Company's Board, she also served as the Chief Compliance Officer and Secretary of the Company since 2015. Prior to joining Sixth Street, from 2004 to 2014, she held various positions at Goldman, Sachs & Co., including most recently as a Managing Director co-heading

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Americas Securities Division Compliance. Ms. Gordon was previously an associate at the law firm of White & Case LLP. Ms. Gordon holds a J.D. from Fordham University School of Law and B.A. in International Relations from the University of Michigan. Ms. Gordon's regulatory and operational knowledge provides the Board with valuable insight in the financial services sector.

Judy Slotkin was elected a director of TSLX in September 2019. Ms. Slotkin retired as a Managing Director from Bank of America in 2015, where she most recently led business development and relationship management for the New York market as part of the Market Executive team in private wealth management. Prior to joining Bank of America in 2010, Ms. Slotkin served as the Chief Risk Officer at Everspan Financial Guaranty. Prior to joining Everspan, Ms. Slotkin served various leadership roles at Citigroup, including Department Head of the Corporate Finance Division, where she led origination, trading and sales of asset-backed securities, commercial paper on an agency basis, loan note trading and investment grade loan syndications. During her career at Citigroup, Ms. Slotkin also served as the Credit Head of the Corporate Finance Division and Municipal Credit Head of Public Finance. Ms. Slotkin holds a B.S. in Accounting from Fairleigh Dickinson University and an M.B.A. in Finance from Fordham University. She currently serves on the board and as chair of the audit committee of Sixth Street Lending Partners and she previously served as a director, chair of the nominating and corporate governance committee and a member of the audit committee for Siga Technologies, Inc. and a director and chair of the audit committee for Nephros, Inc. Ms. Slotkin's numerous management positions and broad experiences within financial institutions provide the Board and, specifically, the Audit Committee, which she chairs, with valuable knowledge and insight in the financial services sector.

P. Emery Covington was appointed a director in July 2023. Ms. Covington retired as an Executive Vice President and Head of Commercial Credit Risk at Truist Bank (formerly SunTrust Bank), leading a credit execution team from 2009 through 2020 spanning a diversified exposure of businesses across the SunTrust footprint. She also served as a member of the Senior Credit Committee. Prior to joining SunTrust, Ms. Covington was a Managing Director at NewStar Financial from 2004, creating the Portfolio Management platform. Prior to joining NewStar Financial, Ms. Covington served in various leadership and credit-oriented roles at Fleet Boston Financial Group over a period of 24 years, most recently as Executive Vice President. Ms. Covington began her career as part of the Corporate Bank loan officer and management training program at Chemical Bank. Ms. Covington holds an A.B. in English (cum laude with Honors) from Smith College. She previously served on the Board of Risk Management Associates, including as Chair of the Professional Development Council and the Specialized Lending Council, and on the Board of the Women and Infants Foundation Board in Providence, Rhode Island. Ms. Covington's numerous management positions and broad experiences within financial institutions provide the Board with valuable knowledge and insight in the financial services sector.

Incumbent Class III Directors: Term Expiring 2026

Hurley Doddy was elected a director of TSLX in January 2019. Mr. Doddy is a Managing Director, Founding Partner and Chief Executive Officer of Emerging Capital Partners, a private equity fund manager focused on Africa. Prior to founding Emerging Capital Partners in 1999, Mr. Doddy was an Executive Director at Sumitomo Finance International in London. Mr. Doddy's career in finance began at Salomon Brothers in 1984, lasting over 14 years with assignments in New York, Tokyo, and Sao Paulo. He also currently serves on the board of Sixth Street Lending Partners. Mr. Doddy holds an A.B. in Economics from Princeton University and a Chartered Financial Analyst (CFA) designation. Mr. Doddy's breadth of experience across financial markets and products, geographies, along with his focus on risk management, provides the Board with valuable insight and perspective in the credit sector.

Joshua Easterly was appointed Chief Executive Officer of TSLX in January 2018 and elected a director and Chairman of TSLX in March 2011. Prior to his appointment, Mr. Easterly served as a Vice President of TSLX since March 2011 and as the Co-ChiefExecutive Officer of TSLX since December 2013, along with Michael Fishman. Mr. Easterly is also Chief Executive Officer, a trustee and Chairman of the board of Sixth Street Lending Partners. Mr. Easterly is a Co-Founder,Partner and Co-President,and the Co-ChiefInvestment

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Officer of Sixth Street. Between 2008 and 2010, he was a Managing Director at Goldman, Sachs & Co. in the Americas Special Situations Group, which invested Goldman's capital in both the public markets and private transactions in distressed and special situations. Between 2006 and 2008, he served as a Director, Management Committee Member and Co-Headof the Goldman Sachs Specialty Lending Group. Prior to joining Goldman, Sachs & Co. in March 2006, Mr. Easterly was Senior Vice President, Northeast Regional Originations Manager at Wells Fargo Capital Finance, or WFCF, formerly known as Wells Fargo Foothill and Foothill Capital Corporation, the commercial finance company of Wells Fargo and Company. Mr. Easterly graduated from California State University, Fresno with a Bachelor of Science in Business Administration, magna cum laude. Mr. Easterly's depth of experience investing in a variety of distressed and special situations transactions as well as his extensive knowledge of the business and operations of Sixth Street provides the Board with valuable insight and expertise.

Michael Fishman was elected a director of TSLX in April 2011. From April 2011 to December 2013, he served as Chief Executive Officer, and from December 2013 to December 2017, he served as Co-ChiefExecutive Officer with Joshua Easterly. Mr. Fishman is a Vice President of TSLX and is a Partner of Sixth Street. He has been an executive in corporate lending for more than 30 years with senior management experience in credit, portfolio management and primary loan originations. Prior to joining TSLX, Mr. Fishman was the Executive Vice President and National Director of Loan Originations for WFCF, formerly known as Wells Fargo Foothill and Foothill Capital Corporation. In this role, Mr. Fishman sat on the senior investment committee and was responsible for primary and secondary lending, loan distribution and syndications, strategic transactions and new lending products. From 2000 to 2007, he built the team that grew WFCF's assets under management from approximately $2 billion to over $10 billion. Mr. Fishman has also contributed to various industry publications and panel discussions, and has sat on the board of the American Bankruptcy Institute. He holds a B.S. in Finance from Rochester Institute of Technology. Mr. Fishman's extensive experience in the credit markets provides the Board with valuable industry-specific knowledge.

Incumbent Class I Directors: Term Expiring 2027

Richard Higginbotham was elected a director of TSLX in March 2011. From September 2010, he was a director of Healthcare Finance Group LLC until its sale in 2013. Between July 2008 and March 2010, Mr. Higginbotham was a director and then chairman of Tygris Commercial Finance Group, Inc., where he also served on the risk committee. From 2004 to 2005, Mr. Higginbotham was the President of Asset Based Lending and Leasing at Bank of America. Prior to that, he worked for 35 years, including in various senior executive positions, at Fleet Bank, Fleet Financial Group, Inc. and FleetBoston Financial, Inc. He also currently serves on the board of Sixth Street Lending Partners. Mr. Higginbotham holds a B.A. in Political Science from Brown University. Mr. Higginbotham's depth of experience in senior executive positions in the financial sector provides the Board with valuable experience, insight and perspective in the credit sector.

David Stiepleman was elected a director of TSLX in September 2019. Mr. Stiepleman is a Vice President of TSLX. He is a Co-Founder,Partner and Co-Presidentof Sixth Street. Mr. Stiepleman has been a cross-border corporate lawyer, senior executive and business builder for over 25 years, starting and running businesses, and representing clients, in the U.S., Europe and Asia. Mr. Stiepleman currently serves on the board of Sixth Street Lending Partners and is a strategic advisor to Westbound Equity Partners (f/k/a Concrete Rose). He also serves on the Advisory Council for Mt. Tamalpais College, a college-degree awarding program at San Quentin Prison. Mr. Stiepleman received a B.A. in French and Political Science from Amherst College and a J.D. from Columbia University. Mr. Stiepleman's legal, regulatory and operational experience provides the Board with valuable knowledge and guidance.

Ronald Tanemura was elected a director of TSLX in March 2011. Mr. Tanemura currently serves on the boards of post-reorganization Lehman Brothers Holdings Inc., Sixth Street Lending Partners, and of Talcott Resolution Life Insurance Company and certain affiliates. Also, from 2012 to 2019, he served as a non-executivedirector of ICE Clear Credit in Chicago and, from 2009 to 2019, he served as a non-executivedirector of ICE

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Clear Europe in London, both wholly owned subsidiaries of Intercontinental Exchange, Inc. Prior to that, Mr. Tanemura was an Advisory Director and Partner at Goldman, Sachs & Co. from 2000 to 2006 where he was the Global Co-Headof Credit Derivatives and a member of the Fixed Income, Currency and Commodities Risk Committee and Firmwide Credit Policy Committee. In addition, Mr. Tanemura has led a variety of fixed income businesses, working at Deutsche Bank from 1996 to 2000 and at Salomon Brothers from 1985 to 1996. Mr. Tanemura holds an A.B. in Computer Science from the University of California, Berkeley. Mr. Tanemura's extensive experience in the financial markets provides the Board with valuable industry-specific knowledge.

Equity Owned by Directors and Nominees in the Company

The following table sets forth the dollar range of equity securities of the Company beneficially owned by each director or director nominee as of March 31, 2025. The Company is not part of a "family of investment companies," as that term is defined in the 1940 Act.

Litigation Involving Directors and Nominees Adverse to the Company

None.

Information Regarding Executive Officers Who Are Not Directors

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Anton Brett is the Chief Compliance Officer and Secretary of TSLX and a Managing Director of Sixth Street. Prior to joining Sixth Street, from 2017 to 2020, he was a Senior Associate at Scopia Capital Management, LP. From 2014 to 2017, Mr. Brett was an Associate at the law firm of Willkie Farr & Gallagher LLP. From 2009 to 2011, he was an Analyst, and later a Senior Analyst, at the law firm of Kobre & Kim LLP. Mr. Brett holds a J.D. from Duke University School of Law and B.A. in International Relations and Slavic Studies, magna cum laude, from Brown University.

Michael Graf is a Managing Director and Deputy Chief Financial Officer of TSLX. From 2010 to 2013, Mr. Graf was a Vice President in Alternative Investments at U.S. Bancorp Fund Services, LLC. From 2006 to 2010, Mr. Graf was an Accounting Manager at GSC Group, Inc., a private investment firm. Prior to working at GSC Group Inc., Mr. Graf worked in public accounting at KPMG from 2004 to 2006. Mr. Graf holds a B.S. in Finance and Accounting from the Leonard N. SteSchool of Business at New York University. He is a Certified Public Accountant.

Craig Hamrah is a Vice President of TSLX, Senior Credit Underwriter of the Adviser and a Partner of Sixth Street. Mr. Hamrah was previously with Silver Point Capital, where he was a senior deal underwriter and oversaw the portfolio in the private finance group. From 2004 to 2005, Mr. Hamrah was a Senior Vice President at the Royal Bank of Scotland. From 1997 to 2004, Mr. Hamrah was an Executive Vice President at Emigrant Business Credit Corp, a subsidiary of Emigrant Savings Bank. Mr. Hamrah started his career at The CIT Group in 1990 working in the commercial finance and equipment finance divisions. He holds a B.A. in Business Economics from Brown University.

Joshua Peck is a Vice President of TSLX and a Partner and General Counsel of Sixth Street. Prior to joining Sixth Street in 2015, Mr. Peck was an Associate with Weil, Gotshal & Manges LLP, focused on private equity and mergers and acquisitions. He holds a J.D. from Fordham Law School and a B.A. in Government from Cornell University. Mr. Peck serves on the Board of Directors of Legal Aid at Work, a non-profitlegal services organization that has been assisting low-income,working families for more than 100 years. Licensed only in New York. Registered In-HouseCounsel in California.

Steven Pluss is a Vice President of TSLX. He is a Co-Founderand Partner of Sixth Street and has also been the Chief Risk Officer since 2013, as well as the Chief Financial Officer from 2013 to 2016. Prior to joining Sixth Street, Mr. Pluss was a Managing Director and co-headof the Goldman Sachs Specialty Lending Group at Goldman, Sachs & Co., where he worked from 2004 to 2013. From 1999 to 2004, Mr. Pluss was a Partner,

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Founder and Managing Member of RTV Ventures, a special situations lending joint venture with Goldman, Sachs & Co. Mr. Pluss holds a B.B.A. from Texas A&M University and an M.B.A. from SoutheMethodist University.

Ian Simmonds is the Chief Financial Officer of TSLX and a Partner of Sixth Street. He is also the Chief Financial Officer of Sixth Street Lending Partners. From 2005 to 2015, Mr. Simmonds was a member of the Financial Institutions Group at Bank of America Merrill Lynch's Global Investment Bank in New York, most recently as a Managing Director. From 2000 to 2003, Mr. Simmonds was Managing Director at Principal Global Investors, the asset management unit of The Principal Financial Group, based in Singapore. Prior to this role, Mr. Simmonds was at Bankers Trust Australia from 1995 to 2000 (acquired by Principal in 1999), and at KPMG from 1989 to 1995. Mr. Simmonds holds a Bachelor of Commerce from the University of New South Wales, a Master of Applied Finance from Macquarie University, and an M.B.A. from the Wharton School of the University of Pennsylvania. He is a Chartered Accountant.

Robert ("Bo") Stanley is President of TSLX, a Partner of Sixth Street, and Co-Headof Sixth Street Growth. Mr. Stanley focuses on originating transactions in the software, payment systems, data infrastructure and business services sectors. Mr. Stanley was previously with Wells Fargo Capital Finance, a provider of specialized senior secured financing to companies throughout the U.S. and Canada, from 2000 to 2011. While at Wells Fargo, Mr. Stanley served in multiple roles in an underwriting and origination capacity. He holds a B.S. in Business Administration with a concentration in Finance from the University of Maine.

Alan Waxman is a Vice President of TSLX. Mr. Waxman is a Co-Founder,Partner and Chief Executive Officer of Sixth Street. Prior to co-foundingSixth Street, Mr. Waxman was a Partner at Goldman, Sachs & Co. and Chief Investment Officer of its largest proprietary investing business, the Americas Special Situations Group. Sixth Street continues an investment philosophy Mr. Waxman and Sixth Street's founding partner group began developing over 20 years ago while building complementary businesses to invest Goldman's capital in public and private markets across the capital structure in companies, assets, and idiosyncratic opportunities. Mr. Waxman is a Founding LP and Strategic Advisor to Westbound Equity Partners (f/k/a Concrete Rose). He and other Sixth Street team members began advising Westbound Equity Partners leadership on the firm's formation in 2018 and Sixth Street is a Founding Strategic Partner. Mr. Waxman holds a B.A. in International Relations from the University of Pennsylvania and currently serves on the Board of Overseers for the University of Pennsylvania College of Arts and Sciences. He is a Board Member Emeritus for Tipping Point Community and serves on the Advisory Council for the Boys and Girls Club of the Peninsula.

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CORPORATE GOVERNANCE

Our Board of Directors

Board Composition

Our Board currently consists of ten members, and, following Mr. Ross's retirement at the close of business on May 22, 2025, will consist of nine members. Pursuant to our bylaws, the Board may increase or decrease the number of directors to no fewer than four and no greater than ten. The Board is divided into three classes, with the members of each class each serving staggered, three-year terms. The terms of our Class III directors will expire at the 2026 annual meeting of stockholders; the terms of our Class I directors will expire at the 2027 annual meeting of stockholders; and the terms of our Class II directors will expire at the Meeting.

Independent Directors

Pursuant to our certificate of incorporation, a majority of the Board will at all times consist of directors who are not "interested persons" of us, of the Adviser, or of any of our or its respective affiliates, as defined in the 1940 Act. Under Section 303A.00 of the NYSE Listed Company Manual, a director of a business development company ("BDC") is considered to be independent if he or she is not an "interested person" of ours, as defined in Section 2(a)(19) of the 1940 Act. We refer to these directors as our "Independent Directors."

Consistent with these considerations, after review of all relevant transactions and relationships between each director, or any of his or her family members, and us, the Adviser, or of any of our or its respective affiliates, the Board has determined that Messrs. Doddy, Higginbotham, Ross and Tanemura and Mses. Slotkin and Covington qualify as Independent Directors. Each director who serves on the Audit Committee is an independent director under the applicable NYSE listing standards and for purposes of Rule 10A-3under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Each director who serves on the Compensation Committee and Nominating and Corporate Governance Committee is an independent director under the applicable NYSE listing standards. A majority of the voting members of the Risk Management Committee are Independent Directors.

Interested Directors

Messrs. Easterly, Fishman, Stiepleman and Ms. Gordon are considered "interested persons" (as defined in the 1940 Act) of the Company since all of them are employed by the Adviser. See "Proposal No. 1 Election of Directors - Biographical Information."

Meetings and Attendance

Our Board met four times in 2024 and acted on various occasions by written consent. Our Board also holds informal periodic telephonic update meetings. No incumbent director attended fewer than 75% of the aggregate of the total number of meetings of the Board (held during the period for which he or she has been a director) and the total number of meetings held by all committees of the Board on which he or she served (during the periods that he or she served).

Board Attendance at the Meeting

Our policy is to encourage our directors to attend each annual meeting of stockholders; however, attendance is not required. Mr. Easterly attended the 2024 annual meeting of stockholders.

Board Leadership Structure and Role in Risk Oversight

Our Board monitors and performs an oversight role with respect to our business and affairs, including with respect to investment practices and performance, compliance with regulatory requirements, cybersecurity and the services, expenses and performance of service providers to us. Among other things, our Board approves the appointment of our Adviser and our officers, reviews and monitors the services and activities performed by our investment adviser and our executive officers.

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Our Board designates a chairman to preside over the meetings of the Board and to perform other duties as may be assigned to him by the Board. We do not have a fixed policy as to whether the chairman of the Board should be an Independent Director and believe that we should maintain the flexibility to select the chairman and reorganize the leadership structure, from time to time, based on the criteria that is in our best interests and the best interests of our stockholders at such times.

Presently, Mr. Easterly serves as the chairman of our Board. We believe that Mr. Easterly's familiarity with our investment platform and extensive knowledge of the financial services industry qualifies him to serve as the chairman of our Board.

Our Board does not currently have a designated lead Independent Director. We are aware of the potential conflicts that may arise when a non-IndependentDirector is chairman of the Board, but believe these potential conflicts are offset by our strong corporate governance practices. Our corporate governance practices include regular meetings of the Independent Directors in executive session without the presence of interested directors and management, as well as the establishment of a Nominating and Corporate Governance Committee, a Compensation Committee and an Audit Committee, each consisting solely of Independent Directors for the purposes of the NYSE corporate governance rules and, in the case of the Audit Committee, Rule 10A-3under the Exchange Act. During executive sessions, the Chair of the Audit Committee or her designee acts as presiding director. We also have a Risk Management Committee, a majority of the voting members of which are Independent Directors. In addition, our corporate governance practices include the appointment of our Chief Compliance Officer, with whom the Independent Directors meet in executive session without the presence of interested directors and other members of management for administering our compliance policies and procedures. While certain non-managementmembers of our Board currently participate on the boards of directors of other companies, we do not view their participation as excessive or as interfering with their duties on our Board.

Our Board performs its risk oversight function primarily through (i) its standing committees, which report to the entire Board and (ii) active monitoring by our Chief Compliance Officer in accordance with its compliance policies and procedures.

As described below in more detail under "-Board Committees-Audit Committee," the Audit Committee assists the Board in fulfilling its risk oversight responsibilities. The Audit Committee's risk oversight responsibilities include overseeing our accounting and financial reporting processes, our systems of internal controls regarding finance and accounting, and audits of our financial statements. The Audit Committee also discusses with management our major financial risk exposures and the steps management has taken to monitor and control such exposures, including our risk assessment and risk management policies.

In addition, as described below under "-Board Committees-Risk Management Committee," the Risk Management Committee assists the Board in its oversight of our overall risk tolerance and management of capital, liquidity, and funding planning and strategy. In performing its responsibilities, the Risk Management Committee liaises with the Chair of the Audit Committee to assist that committee in its review of our risk assessment and risk management matters.

Our Board also performs its risk oversight responsibilities with the assistance of the Chief Compliance Officer. Our Chief Compliance Officer prepares a written report annually discussing the adequacy and effectiveness of our compliance policies and procedures. The Chief Compliance Officer's report, which is reviewed by the Board, addresses:

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In addition, the Chief Compliance Officer meets separately in executive session with the Independent Directors periodically, typically every quarter, but in no event less than once each year.

We believe that the Board's role in risk oversight is effective and appropriate given the extensive regulation to which we are already subject as a BDC. Specifically, as a BDC, we must comply with numerous regulatory requirements that control the levels of risk in its business and operations, including limitations under the 1940 Act on the amount of borrowings, debt securities or preferred stock we may incur or issue and we are limited in our ability to enter into transactions with our affiliates, including investing in any portfolio company in which one of our affiliates currently has an investment. In addition, we generally have to invest at least 70% of our total assets in "qualifying assets" and, subject to certain exceptions, we generally are not permitted to invest in any portfolio company in which our affiliates currently has an investment. In addition, we have elected to be treated as a regulated investment company ("RIC") under Subchapter M of the Internal Revenue Code of 1986, as amended (the "Code"). As a RIC, we must, among other things, meet certain source of income, asset diversification and distribution requirements.

Oversight of our investment activities extends to oversight of the risk management processes employed by the Adviser as part of its day-to-daymanagement of our investment activities. The Board reviews risk management processes at both regular and special board meetings throughout the year, consulting with appropriate representatives of the Adviser as necessary and periodically requesting the production of risk management reports or presentations. The goal of the Board's risk oversight function is to ensure that the risks associated with our investment activities are accurately identified, thoroughly investigated and responsibly addressed. Investors should note, however, that the Board's oversight function cannot eliminate all risks or ensure that particular events do not adversely affect the value of investments.

Further, we believe that the Board's structure and practices enhance its risk oversight because our Independent Directors separately meet in executive sessions with the Chief Compliance Officer and independent registered public accounting firm without any conflict that could be perceived to discourage critical review.

We believe that the Board's role in risk oversight must be evaluated on a case-by-casebasis and that its existing role in risk oversight is appropriate.

Communications with Directors

Our Board has established procedures whereby our stockholders and other interested parties may communicate with any member of our Board, the chairman of any of our Board committees or with our non-managementdirectors as a group by mail addressed to the applicable directors or director group, in the care of the Chief Compliance Officer, Anton Brett, Sixth Street Specialty Lending, Inc., 888 7th Avenue, 41st Floor, New York, NY 10106. Such communications should specify the intended recipient or recipients. All such communications, other than unsolicited commercial solicitations, will be forwarded to the appropriate director, or directors, for review.

In addition, information on how to report issues related to financial statement disclosures, accounting, internal accounting controls or auditing matters to our Board or the Independent Directors via email is available on our website at https://sixthstreetspecialtylending.gcs-web.com/corporate-governance.

Board Committees

We currently have four standing committees: the Audit Committee, the Nominating and Corporate Governance Committee, the Compensation Committee and the Risk Management Committee.

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Audit Committee

The Audit Committee operates pursuant to the Audit Committee Charter. The Audit Committee Charter sets forth the responsibilities of the Audit Committee. The primary function of the Audit Committee is to serve as an independent and objective party to assist the Board in fulfilling its responsibilities for our accounting and reporting processes and the audits of its financial statements by overseeing and monitoring:

Our Audit Committee has the sole authority to approve the engagement, and review the performance of, our independent registered public accounting firm.

Our Board has designated Ms. Slotkin as an "audit committee financial expert" pursuant to the provisions of Item 407(d)(5) of Regulation S-K,and, pursuant to the Audit Committee Charter, our Audit Committee consists solely of members who are independent directors for the purposes of the applicable NYSE corporate governance rules and Rule 10A-3under the Exchange Act.

Messrs. Doddy, Higginbotham, Ross, Ms. Slotkin and Mr. Tanemura are members of the Audit Committee and Ms. Slotkin serves as Chair. The Audit Committee held eight meetings in 2024.

Nominating and Corporate Governance Committee

The Nominating and Corporate Governance Committee operates pursuant to the Nominating and Corporate Governance Committee Charter. The Nominating and Corporate Governance Committee Charter sets forth the responsibilities of the Nominating and Corporate Governance Committee. The Nominating and Corporate Governance Committee is responsible for:

The Nominating and Corporate Governance Committee considers nominees to the Board recommended by a stockholder, if that stockholder complies with the advance notice provisions of our bylaws, as described below.

The members of the Nominating and Corporate Governance Committee are Messrs. Doddy, Higginbotham, Ross, and Tanemura and Mses. Slotkin and Covington, each of whom is independent for purposes of the NYSE corporate governance rules, and each of whom is not an "interested person" of the Company, of the Adviser, or of any of their respective affiliates as defined in Section 2(a)(19) of the 1940 Act. Mr. Higginbotham serves as Chairman. The Nominating and Corporate Governance Committee held one meeting in 2024.

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Compensation Committee

The Compensation Committee operates pursuant to the Compensation Committee Charter. The Compensation Committee Charter sets forth the responsibilities of the Compensation Committee. The Compensation Committee is responsible for:

See "-Compensation and Insider Participation-Compensation of Executive Officers."

The members of the Compensation Committee are Messrs. Doddy, Higginbotham, Ross, and Tanemura and Mses. Slotkin and Covington, each of whom is independent for purposes of the NYSE corporate governance rules. Mr. Ross serves as Chairman. The Compensation Committee held three meetings in 2024.

Risk Management Committee

The Risk Management Committee operates pursuant to the Risk Management Committee Charter. The Risk Management Committee Charter sets forth the responsibilities of the Risk Management Committee. The Risk Management Committee is responsible for assisting the Board in its oversight of the Company's overall risk tolerance and management of capital, liquidity, and fund planning and strategy. Risk assessment and risk management are the primary responsibility of the Company's management. The Risk Management Committee's responsibility is one of oversight and review, in furtherance of the Board's oversight role.

The voting members of the Risk Management Committee are Messrs. Easterly, Ross and Tanemura, and the non-votingmembers of the committee are Messrs. Simmonds and Pluss. Messrs. Ross and Tanemura are independent for purposes of the NYSE corporate governance rules. Mr. Easterly serves as Chairman. The Risk Management Committee held four meetings in 2024, which were held jointly with a meeting of the full board.

Committee Charters

We maintain a corporate governance section on our website, which contains copies of the charters for the committees of our Board. The corporate governance section may be found at http://www.sixthstreetspecialtylending.com in the "Investor Resources" section of our website. The corporate governance section contains the following documents:

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Certain Relationships and Related Party Transactions

Transactions with Related Persons

Relationship with Sixth Street

Our investment activities are managed by our Adviser, which is responsible for sourcing, researching and structuring potential investments, monitoring our portfolio companies and providing operating, managerial and administrative assistance to us and to our portfolio companies as required.

The Adviser is registered under the Advisers Act and is an affiliate of Sixth Street. Other affiliates of Sixth Street are also registered investment advisers and provide investment advisory services to a number of private investment funds. In addition, Sixth Street and its affiliates engage in a broad range of other investment activities, including pursuing investments for their own account and for the account of associated funds and providing other services to these funds and their portfolio companies. Sixth Street manages another BDC targeting loan originations of larger size than the originations that we target. The Adviser held 2,714,226 shares, or 2.9%, of our common stock as of March 31, 2025.

We believe we benefit from the Adviser's relationships with Sixth Street. The Adviser has access to the contacts and industry knowledge of Sixth Street's investment professionals, and is also able to consult with Sixth Street investment professionals on specific industry issues, trends and other matters to complement our investment process. However, the Adviser and members of the Investment Review Committee are expected to face a number of actual and potential conflicts of interest involving us, Sixth Street and other private investment funds affiliated with Sixth Street, including conflicts in the allocation of investment opportunities among us and other Sixth Street vehicles, as well as in their time and attention requirements as to these other vehicles. Additionally, various potential and actual conflicts of interest may arise from the overall advisory, investment and other activities of the Adviser, its affiliates, including Sixth Street and its clients.

Allocations of Investment Opportunities

Certain members of the Adviser's senior management and the Investment Review Committee are and will continue to be active in other investment funds affiliated with Sixth Street that pursue investment opportunities that could overlap with those pursued by us. However, the Adviser and its affiliates intend to allocate investment opportunities in a fair and equitable manner in accordance with their allocation principles.

As described in more detail below, the SEC granted us a new exemptive order in August 2022, pursuant to which Sixth Street must generally make us aware of all investment opportunities that fall within certain criteria established by our Board from time to time pursuant to the terms of the order, which we refer to as the "Board Established Criteria". Our Adviser will ultimately determine whether an investment opportunity is appropriate for us in view of our investment objectives, positions, policies, strategies and restrictions, as well as regulatory requirements and other relevant factors.

Specifically, the Adviser will determine whether it would be permissible, advisable or otherwise appropriate for us to pursue a particular investment opportunity. For example, certain loan origination investment opportunities may not be suitable for us if they would cause us to violate asset coverage or concentration limitations imposed by the 1940 Act or the Code, be ineligible for financing under our financing arrangements, pose adverse legal, regulatory or tax risks, constrain our resources to make future investments, involve inappropriate investment risk or otherwise be inappropriate or inadvisable as an investment for us. If the Adviser deems participation in an investment opportunity to be appropriate, it will determine an appropriate size for our investment. The size of any investment opportunity allocated to us may also be reduced to the extent the investment would be appropriate for investment by other investment funds affiliated with Sixth Street, even if the investment falls within our Board Established Criteria. The decision to allocate an opportunity as between us and other Sixth Street vehicles will take into account various factors that Sixth Street and our Adviser deem appropriate.

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Our ability to pursue investment opportunities is subject to the allocation decisions by Sixth Street senior professionals. Such opportunities may be required to be offered to, or may be otherwise suitable for, other Sixth Street funds or investment vehicles. As a result, the Adviser and its affiliates may face conflicts in allocating investment opportunities between us and those other entities. It is possible that we may not be given the opportunity to participate in certain investments made by Sixth Street vehicles that would otherwise be suitable for us. We will typically not be able to participate under the exemptive order in investments that fall outside of our Board Established Criteria. Sixth Street has organized separate investment vehicles, aimed specifically at middle-market loan originations and may in the future organize vehicles aimed at other loan origination opportunities outside our primary focus (for example, based on opportunity size or geography).

If the Adviser, Sixth Street and their affiliates were to determine that an investment is appropriate both for us and for one or more other affiliated vehicles, we would only be able to make the investment in conjunction with another vehicle to the extent the exemptive order granted to us by the SEC permits us to do so or the investment is otherwise permitted under relevant SEC guidance.

The Adviser believes this allocation system is fair and equitable, and consistent with its fiduciary duty to us. In particular, we have disclosed to investors that Sixth Street must make us aware of all investment opportunities that fall within our Board Established Criteria. In addition, we have disclosed how allocation determinations are made among Sixth Street vehicles in connection with such opportunities, including those circumstances in which the Adviser may be required to offer them to these affiliated vehicles.

Exemptive Order

Under the 1940 Act, we are prohibited from knowingly participating in certain transactions with our affiliates, including our officers, directors, investment adviser, and principal underwriters, and certain of their affiliates, without the prior approval of the members of our Board who are not interested persons and, in some cases, prior approval by the SEC through an exemptive order (other than in certain limited situations pursuant to current regulatory guidance).

On December 16, 2014, we were granted an exemptive order from the SEC that allows us to co-invest,subject to certain conditions and to the extent the size of an investment opportunity exceeds the amount our Adviser has independently determined is appropriate for us to invest, with certain of our affiliates (including affiliates of Sixth Street) in middle-market loan origination activities for companies domiciled in the United States and certain "follow-on"investments in companies in which we have already co-investedpursuant to the order and remain invested. On January 16, 2020, we filed a further application for co-investmentexemptive relief with the SEC to better align our existing co-investmentrelief with more recent SEC exemptive orders. Subsequent further applications were also made, most recently as June 29, 2022. On August 3, 2022, the SEC granted an amended exemptive order in response to our application.

We believe our ability to co-investwith Sixth Street affiliates is particularly useful where we identify larger capital commitments than otherwise would be appropriate for us. We expect that with the ability to co-investwith Sixth Street affiliates we will continue to be able to provide "one-stop"financing to a potential portfolio company in these circumstances, which may allow us to capture opportunities where we alone could not commit the full amount of required capital or would have to spend additional time to locate unaffiliated co-investors.

Further, in accordance with the exemptive order, we have undertaken that, in connection with any commitment to a co-investmentor follow-oninvestment, a "required majority" (as defined in Section 57(o) of the 1940 Act) of Independent Directors must make certain conclusions, including that:

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Allocation of Non-LoanOrigination Investment Opportunities

While we seek to generate current income primarily in U.S.-domiciled middle-market companies through direct originations of senior secured loans, we may also invest up to 30% of our portfolio opportunistically in securities or other instruments of issuers not deemed eligible portfolio companies under the 1940 Act. These opportunities may include, among other things, debt issued by companies located outside the United States, publicly and privately traded debt and equity securities of companies listed on a national securities exchange with a market capitalization of $250 million or more, certain high yield bonds and other instruments or assets (including consumer and commercial loans). Many of these opportunities may be required to be offered to, or may be otherwise suitable for, other Sixth Street funds or investment vehicles, in which case the scope or size of opportunities otherwise available to us may be adversely affected or reduced. In the event that an investment opportunity falls within our Board Established Criteria and Sixth Street is not required to, and otherwise determines not to, direct these investment opportunities to an affiliated fund, we may be permitted to participate in such investment opportunity under the terms of our current exemptive order.

Administrator

The Adviser also serves as our administrator. The administrator, on behalf of us and at our expense, may retain one or more service providers that may also be affiliates of Sixth Street to serve as sub-administrator,custodian, accounting agent, investor services agent, transfer agent or other service provider for us. Any fees we pay, or indemnification obligations we undertake, in respect of the administrator and those other service providers that are Sixth Street affiliates, will be set at arm's length and approved by the Independent Directors.

Fees

In the course of our investing activities, we pay fees to the Adviser, incur direct expenses and reimburse the Adviser for certain expenses it incurs.

Certain Business Relationships

Certain of our current directors and officers are directors or officers of the Adviser or its affiliates. See "Proposal No. 1 Election of Directors - Biographical Information."

Related-Party Transactions

Investment Advisory Agreement; Administration Agreement; License Agreement

On April 15, 2011, we entered into the Investment Advisory Agreement with our Adviser. The Investment Advisory Agreement was subsequently amended on December 12, 2011.

Under the Investment Advisory Agreement, the Adviser:

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The Adviser's services under the Investment Advisory Agreement are not exclusive, and the Adviser is free to furnish similar or other services to others so long as its services to us are not impaired.

Under the terms of the Investment Advisory Agreement, we pay the Adviser a base management fee, or the "Management Fee," and may also pay certain incentive fees, or "Incentive Fees".

The Management Fee is calculated at an annual rate of 1.5% based on the average value of our gross assets calculated using the values at the end of the two most recently completed calendar quarters, adjusted for any share issuances or repurchases during the period. The Management Fee is payable quarterly in arrears.

For the year ended December 31, 2024, Management Fees (gross of waivers) were $51.8 million.

Any waived Management Fees are not subject to recoupment by the Adviser.

The Adviser intends to waive a portion of the Management Fee payable under the Investment Advisory Agreement by reducing the Management Fee on assets financed using leverage over 200% asset coverage (in other words, over 1.0x debt to equity) (the "Leverage Waiver"). Pursuant to the Leverage Waiver, the Adviser intends to waive the portion of the Management Fee in excess of an annual rate of 1.0% (0.250% per quarter) on the average value of our gross assets as of the end of the two most recently completed calendar quarters that exceeds the product of (i) 200% and (ii) the average value of our net asset value at the end of the two most recently completed calendar quarters. For the year ended December 31, 2024, Management Fees of $1.5 million were waived pursuant to the Leverage Waiver. Any waived Management Fees are not subject to recoupment by the Adviser pursuant to the Leverage Waiver.

The Incentive Fee consists of two parts, as follows:

Pre-IncentiveFee net investment income means dividends, interest and fee income accrued by us during the calendar quarter, minus our operating expenses for the quarter (including the Management Fee, expenses payable under the Administration Agreement to the Administrator, and any interest expense and dividends paid on any issued and outstanding preferred stock, but excluding the Incentive

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Fee). Pre-IncentiveFee net investment income includes, in the case of investments with a deferred interest feature (such as original issue discount, debt instruments with pay-in-kindinterest and zero coupon securities), accrued income that we may not have received in cash. Pre-IncentiveFee net investment income does not include any realized capital gains, realized capital losses or unrealized capital gains or losses.

For purposes of determining whether pre-IncentiveFee net investment income exceeds the hurdle rate, pre-IncentiveFee net investment income is expressed as a rate of retuon the value of our net assets at the end of the immediately preceding calendar quarter.

Pre-IncentiveFee net investment income does not include any realized capital gains, realized capital losses or unrealized capital gains or losses. Because of the structure of the Incentive Fee, it is possible that we may pay an Incentive Fee in a quarter in which we incur a loss. For example, if we receive pre-IncentiveFee net investment income in excess of the quarterly minimum hurdle rate, we will pay the applicable Incentive Fee even if we have incurred a loss in that quarter due to realized and unrealized capital losses. In addition, because the quarterly minimum hurdle rate is calculated based on our net assets, decreases in our net assets due to realized or unrealized capital losses in any given quarter may increase the likelihood that the hurdle rate is reached and therefore the likelihood of us paying an Incentive Fee for that quarter. Our net investment income used to calculate this component of the Incentive Fee is also included in the amount of our gross assets used to calculate the Management Fee because gross assets are total assets (including cash received) before deducting liabilities (such as declared dividend payments).

Section 205(b)(3) of the Advisers Act, as amended, prohibits the Adviser from receiving the payment of fees on unrealized gains until those gains are realized, if ever. There can be no assurance that such unrealized gains will be realized in the future. For the year ended December 31, 2024, Incentive Fees were $40.2 million, $45.5 million of which was realized and payable to the Adviser. The Adviser did not waive any Incentive Fees for the year ended December 31, 2024.

Since our IPO, with the exception of its waiver of Management Fees and certain Incentive Fees attributable to our ownership of certain investments and the Leverage Waiver, the Adviser has not waived its right to receive any Management Fees or Incentive Fees payable pursuant to the Investment Advisory Agreement.

In November 2024, the Board renewed the Investment Advisory Agreement. Unless earlier terminated as described below, the Investment Advisory Agreement will remain in effect until November 2025, and may be extended subject to required approvals. The Investment Advisory Agreement will automatically terminate in the event of an assignment and may be terminated by either party without penalty on 60 days' written notice to the other party.

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Our Board monitors the mix and performance of our investments over time and seeks to satisfy itself that the Adviser is acting in our interests and that our fee structure appropriately incentivizes the Adviser to do so.

On March 15, 2011, we entered into the Administration Agreement with our Adviser. Under the terms of the Administration Agreement, the Adviser provides administrative services to us. These services include providing office space, equipment and office services, maintaining financial records, preparing reports to stockholders and reports filed with the SEC, and managing the payment of expenses and the oversight of the performance of administrative and professional services rendered by others. Certain of these services are reimbursable to the Adviser under the terms of the Administration Agreement. See "-Payment of Our Expenses" below. In addition, the Adviser is permitted to delegate its duties under the Administration Agreement to affiliates or third parties and we pay or reimburse the Adviser expenses incurred by any such affiliates or third parties for work done on our behalf. For the year ended December 31, 2024, we incurred expenses of $3.9 million for administrative services payable under the terms of the Administration Agreement.

From time to time, the Adviser may pay amounts owed by us to third-party providers of goods or services, including the Board, and we will subsequently reimburse the Adviser for such amounts paid on our behalf. Amounts payable to the Adviser are settled in the normal course of business without formal payment terms.

In November 2024, the Board renewed the Administration Agreement. Unless earlier terminated as described below, the Administration Agreement will remain in effect until November 2025, and may be extended subject to required approvals. The Administration Agreement may be terminated by either party without penalty on 60 days' written notice to the other party.

No person who is an officer, director or employee of the Adviser or its affiliates and who serves as our director receives any compensation from us for his or her services as a director. However, we reimburse the Adviser or its affiliates for the allocable portion of the costs of compensation, benefits, and related administrative expenses of our officers who provide operational and administrative services to us pursuant to the Administration Agreement, their respective staffs and other professionals who provide services to us (including, in each case, employees of the Adviser or an affiliate). Such reimbursable amounts include the allocable portion of the compensation paid by the Adviser or its affiliates to our Chief Financial Officer, Chief Compliance Officer, and other professionals who provide operational and administrative services to us pursuant to the Administration Agreement, including individuals who provide "back office" or "middle office" financial, operational, legal and/or compliance services to us. We reimburse the Adviser or its affiliates for the allocable portion of the compensation paid by the Adviser or its affiliates to such individuals based on the percentage of time those individuals devote, on an estimated basis, to our business and affairs and in acting on behalf of us. We may also reimburse the Adviser or its affiliates for the allocable portion of overhead expenses (including rent, office equipment and utilities) attributable thereto. Directors who are not affiliated with the Adviser receive compensation for their services and reimbursement of expenses incurred to attend meetings.

The Adviser does not assume any responsibility to us other than to render the services described in, and on the terms of the Investment Advisory Agreement and the Administration Agreement, and is not responsible for any action of our Board in declining to follow the advice or recommendations of the Adviser. Under the terms of the Investment Advisory Agreement and the Administration Agreement, the Adviser (and its members, managers, officers, employees, agents, controlling persons and any other person or entity affiliated with it) shall not be liable to us for any action taken or omitted to be taken by the Adviser in connection with the performance of any of its duties or obligations under the Investment Advisory Agreement, the Administration Agreement or otherwise as an investment adviser of ours (except to the extent specified in Section 36(b) of the 1940 Act concerning loss resulting from a breach of fiduciary duty (as the same is finally determined by judicial proceedings) with respect to the receipt of compensation for services). We shall, to the fullest extent permitted by law, provide indemnification and the right to the advancement of expenses, to each person who was or is made a party or is threatened to be made a party to or is involved (including, without limitation, as a witness) in any actual or threatened action, suit or proceeding, whether civil, criminal, administrative or investigative, by reason

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of the fact that he or she is or was a member, manager, officer, employee, agent, controlling person of the Adviser or any other person or entity affiliated with the Adviser, or is or was a member of the Adviser's Investment Review Committee, on the same general terms set forth in Article VIII of our certificate of incorporation.

United States federal and state securities laws may impose liability under certain circumstances on persons who act in good faith. Nothing in the Investment Advisory Agreement will constitute a waiver or limitation of any rights that we may have under any applicable federal or state securities laws.

We have entered into a License Agreement with Austin IP, LLC that grants us a non-exclusive,royalty-free license to use the mark "Sixth Street" and any derivative thereof.

Payment of Our Expenses

The costs associated with the Investment Team and staff of the Adviser, when and to the extent engaged in providing us investment advisory and management services are paid for by the Adviser. We bear all other costs and expenses of our operations, administration and transactions, including those relating to:

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In addition, from time to time, the Adviser pays amounts owed by us to third-party providers of goods or services, including the Board. We subsequently reimburse the Adviser for those amounts paid on our behalf.

Amounts payable to the Adviser are settled in the normal course of business without formal payment terms. We also reimburse the Adviser for the allocable portion of the compensation paid by the Adviser or its affiliates to our Chief Compliance Officer, Chief Financial Officer, and other professionals who spend time on those related activities (based on the percentage of time those individuals devote, on an estimated basis, to our business and affairs).

Duration and Termination

Unless earlier terminated as described below, both the Investment Advisory Agreement and the Administration Agreement will remain in effect until November 2025, and each may be extended subject to required approvals. Each agreement will remain in effect from year to year thereafter if approved annually by our Board or by the affirmative vote of the holders of a majority of our outstanding voting securities, and, in either case, if also approved by a majority of our Independent Directors. The Investment Advisory Agreement automatically terminates in the event of its assignment, as defined in the 1940 Act, by the Adviser. Each agreement may be terminated by either party without penalty on 60 days' written notice to the other party. The holders of a majority of our outstanding voting securities may also terminate each agreement without penalty on 60 days' written notice.

Indemnification

The Investment Advisory Agreement and the Administration Agreement provide that the Adviser and its members, managers, officers, employees, agents, controlling persons and any other person or entity affiliated with it shall not be liable to us for any action taken or omitted to be taken by the Adviser in connection with the performance of any of its duties or obligations under the Investment Advisory Agreement, the Administration Agreement or otherwise as an investment adviser of ours (except to the extent specified in Section 36(b) of the 1940 Act concerning loss resulting from a breach of fiduciary duty (as the same is finally determined by judicial proceedings) with respect to the receipt of compensation for services). We will, to the fullest extent permitted by law, provide indemnification and the right to the advancement of expenses, to each person who was or is made a party or is threatened to be made a party to or is involved (including, without limitation, as a witness) in any actual or threatened action, suit or proceeding, whether civil, criminal, administrative or investigative, because he or she is or was a member, manager, officer, employee, agent, controlling person or any other person or entity affiliated with the Adviser, including without limitation the Administrator, or is or was a member of the Adviser's Investment Review Committee, on the same general terms set forth in our certificate of incorporation. Our obligation to provide indemnification and advancement of expenses is subject to the requirements of the 1940 Act and Investment Company Act Release No. 11330, which, among other things, preclude indemnification for any liability (whether or not there is an adjudication of liability or the matter has been settled) arising by reason of willful misfeasance, bad faith, gross negligence, or reckless disregard of duties, and require reasonable and fair means for determining whether indemnification will be made.

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Board Approval of the Investment Advisory Agreement

Our Board, including our Independent Directors, and holders of a majority of our outstanding securities, approved our Investment Advisory Agreement in December 2011. Our Board, including a majority of the Independent Directors, renewed the Investment Advisory Agreement in November 2024.

Review, Approval or Ratification of Transactions with Related Persons

The Board conducts quarterly reviews of any potential related party transactions brought to its attention and, during these reviews, it will consider any conflicts of interest brought to its attention pursuant to the Company's compliance policies and procedures. Each of the Company's directors and officers is subject to the Company's Code of Ethics, which places restrictions on related party transactions, and is instructed and periodically reminded to inform the Company's Chief Compliance Officer or his designee of any potential related party transactions. In addition, each such director and executive officer completes a questionnaire on an annual basis designed to elicit information about any potential related party transactions.

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PROPOSAL NO. 2

RATIFICATION OF SELECTION OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

Our Audit Committee has selected KPMG LLP to serve as our independent registered public accounting firm to audit our consolidated financial statements for the year ending December 31, 2025. While the Audit Committee is responsible for the appointment, compensation, retention, termination and oversight of the independent auditor, we are requesting, as a matter of good corporate governance, that the stockholders ratify the appointment of KPMG LLP as the Company's independent registered public accounting firm. If the stockholders fail to ratify the selection, the Audit Committee will reconsider whether to retain KPMG LLP and may retain that firm or another without re-submittingthe matter to our stockholders. Even if the appointment is ratified, the Audit Committee may, in its discretion, direct the appointment of a different independent registered public accounting firm at any time during the year.

KPMG LLP's representatives are expected to be available for the Meeting and will have an opportunity to make a statement, if they so desire, as well as to respond to appropriate questions asked by our stockholders.

The Board recommends that our stockholders vote "FOR" ratification of the selection of KPMG LLP as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2025.

Fees Paid to KPMG LLP

Audit Fees

For the year ended December 31, 2024, the aggregate fees billed by KPMG LLP for the audit of our consolidated financial statements, review of our interim financial statements and other professional services related to SEC registration statements were $840,000. In addition, we reimbursed KPMG LLP $19,906 for out-of-pocketexpenses incurred in the performance of audit services.

For the year ended December 31, 2023, the aggregate fees billed by KPMG LLP for the audit of our consolidated financial statements, review of our interim financial statements and other professional services related to SEC registration statements were $800,000. In addition, we reimbursed KPMG LLP $24,379 for out-of-pocketexpenses incurred in the performance of audit services.

Audit-Related Fees

For the year ended December 31, 2024, the aggregate fees billed by KPMG LLP for audit-related services, which consist of assurance and related services that are reasonably related to the performance of the audit or review of our consolidated financial statements, but which are not reportable as Audit Fees, were $105,000.

For the year ended December 31, 2023, the aggregate fees billed by KPMG LLP for audit-related services, which consist of assurance and related services that are reasonably related to the performance of the audit or review of our consolidated financial statements, but which are not reportable as Audit Fees, were $295,000.

Audit-related services are assurance and related services that are reasonably related to the performance of the audit or review of our financial statements and that are traditionally performed by the independent auditor.

Tax Fees

For the year ended December 31, 2024, the aggregate fees billed by KPMG LLP for tax compliance, tax advice and tax planning services were $237,000.

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For the year ended December 31, 2023, the aggregate fees billed by KPMG LLP for tax compliance, tax advice and tax planning services were $211,000.

Tax services include tax compliance, tax planning and tax advice.

All Other Fees

For each of the years ended December 31, 2024 and 2023, there were no fees billed for services rendered by KPMG LLP not reportable as Audit Fees, Audit-Related Fees or Tax Fees.

The services provided by KPMG LLP described in "Audit-Related Fees," "Tax Fees" and "All Other Fees" above, were approved by the Audit Committee according to applicable SEC rules.

Pre-ApprovalPolicy

The Audit Committee has established a pre-approvalpolicy that describes the permitted audit, audit-related, tax and other services to be provided by KPMG LLP, the Company's independent registered public accounting firm. The policy requires that the Audit Committee pre-approvethe audit and non-auditservices performed by the independent auditor in order to assure that the provision of such service does not impair the auditor's independence.

Any requests for audit, audit-related, tax and other services that have not received general pre-approvalmust be submitted to the Audit Committee for specific pre-approval,irrespective of the amount, and cannot commence until such approval has been granted. Normally, pre-approvalis provided at regularly scheduled meetings of the Audit Committee. The Audit Committee does not delegate its responsibilities to pre-approveservices performed by the independent registered public accounting firm to management.

Auditor Independence

The Audit Committee has considered whether the provision of the above-noted services is compatible with maintaining the independence of the independent registered public accounting firm and has determined that the provision of such services has not adversely affected KPMG LLP's independence.

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AUDIT COMMITTEE REPORT

The Audit Committee of our Board operates under a written charter adopted by the Board. The Audit Committee is currently composed of Messrs. Ross, Doddy, Higginbotham and Tanemura and Mses. Slotkin and Covington.

Management is responsible for the Company's internal controls and the financial reporting process. The Company's independent registered public accounting firm is responsible for performing an independent audit of the Company's financial statements in accordance with the standards of the Public Company Accounting Oversight Board (US) and expressing an opinion on the conformity of those audited financial statements in accordance with accounting principles generally accepted in the United States and for auditing and reporting on the effectiveness of the Company's internal control over financial reporting. The Audit Committee's responsibility is to monitor and oversee these processes. The Audit Committee is also directly responsible for the appointment, compensation and oversight of the Company's independent registered public accounting firm.

Review with Management

The Audit Committee has reviewed the audited financial statements, along with management's assessment of the effectiveness of the Company's internal control over financial reporting, and met and held discussions with management regarding the audited financial statements and its assessment of the effectiveness of the Company's internal control over financial reporting. Management has represented to the Audit Committee that the Company's financial statements were prepared in accordance with accounting principles generally accepted in the United States. The Audit Committee also reviewed the Company's procedures and internal control processes designed to ensure full, fair and adequate financial reporting and disclosures, including procedures for certifications by the Company's Chief Executive Officer and Chief Financial Officer that are required in periodic reports filed by the Company with the SEC. The Audit Committee is satisfied that the Company's internal control system is adequate and that the Company employs appropriate accounting and auditing procedures.

Review and Discussion with Independent Registered Public Accounting Firm

The Audit Committee has reviewed and discussed the Company's audited financial statements, along with management's assessment of the effectiveness of the Company's internal control over financial reporting and KPMG LLP's evaluation of the Company's internal control over financial reporting, with management and KPMG LLP, the Company's independent registered public accounting firm, with and without management present. The Audit Committee included in its review the results of KPMG's examinations, the Company's internal controls and the quality of the Company's financial reporting.

The Audit Committee also has discussed with KPMG matters relating to KPMG's judgments about the quality, as well as the acceptability, of the Company's accounting principles as applied in its financial reporting as required by Public Company Accounting Oversight Board Auditing Standard No. 16, Communications with Audit Committees. In addition, the Audit Committee has discussed with KPMG their independence from management and the Company, as well as the matters in the written disclosures received from KPMG and required by Public Company Accounting Oversight Board Rule 3526, Communication with Audit Committees Concerning Independence. The Audit Committee received a written communication from KPMG confirming their independence and discussed it with them. The Audit Committee discussed and reviewed with KPMG the Company's critical accounting policies and practices, other material written communications to management, and the scope of KPMG's audits and all fees paid to KPMG during the fiscal year. The Audit Committee has adopted guidelines requiring review and pre-approvalby the Audit Committee of audit and non-auditservices performed by KPMG for the Company. The Audit Committee has reviewed and considered the compatibility of KPMG's performance of non-auditservices with the maintenance of KPMG's independence as the Company's independent registered public accounting firm.

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Conclusion

Based on the Audit Committee's discussion with management and the independent registered public accounting firm, the Audit Committee's review of the audited financial statements, the representations of management and the report of the independent registered public accounting firm to the Audit Committee, the Audit Committee recommended that the Board include the audited financial statements in the Company's Annual Report on Form 10-Kfor the year ended December 31, 2024 for filing with the Securities and Exchange Commission. The Audit Committee also recommended the selection of KPMG LLP to serve as the independent registered public accounting firm for the year ending December 31, 2025.

Unless marked to the contrary, the shares represented by the enclosed proxy card will be voted "FOR" ratification of the appointment of KPMG LLP as the Company's independent registered public accounting firm for the fiscal year ending December 31, 2025.

The material contained in the foregoing Audit Committee Report is not "soliciting material," is not deemed "filed" with the SEC, and is not to be incorporated by reference into any filing of the Company under the Exchange Act, whether made before or after the date hereof and irrespective of any general incorporation language in any such filing.

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OTHER BUSINESS

The Board is not aware of any other matter to be submitted at the Meeting. If any other matter properly comes before the Meeting, the persons named in this proxy generally will have discretionary authority to vote the shares thereby represented in accordance with their judgment.

STOCK REPURCHASES

In accordance with Section 23(c)(1) under the 1940 Act, the Company hereby advises you that it may repurchase shares of its common stock from time to time.

STOCKHOLDER PROPOSALS AND NOMINATIONS FOR THE 2026 ANNUAL MEETING OF STOCKHOLDERS

Inclusion of Proposals in Our Proxy Statement and Proxy Card Under the SEC's Rules

Any proposal of a stockholder intended to be included in our proxy statement and form of proxy/voting instruction card for the 2026 annual meeting of stockholders pursuant to Rule 14a-8of the SEC's rules must be received by us at our principal executive offices no later than December 11, 2025. Such proposals must also comply with the requirements as to form and substance established by the SEC if such proposals are to be included in the proxy statement and form of proxy. All proposals should be sent to our principal executive offices addressed to the Secretary of the Company, Anton Brett, Sixth Street Specialty Lending, Inc., 2100 McKinney Avenue, Suite 1500, Dallas, TX 75201.

Bylaw Requirements for Stockholder Submission of Nominations and Proposals

A stockholder recommendation for nomination of a person for election to our Board or a proposal for consideration at our 2026 annual meeting, other than stockholder proposals submitted pursuant to the SEC's Rule 14a-8,must be submitted in accordance with the advance notice procedures and other requirements set forth in our bylaws. These requirements are separate from the requirements discussed above to have the stockholder nomination or other proposal included in our proxy statement and form of proxy/voting instruction card pursuant to the SEC's rules. The item to be brought before the meeting must be a proper subject for stockholder action.

Our bylaws require that the proposal or recommendation for nomination must be received by our Secretary at our principal executive offices at the above address no later than February 21, 2026, unless the date of our 2026 annual meeting is more than 30 days before or more than 60 days after May 22, 2026, the anniversary of our 2025 annual meeting, in which case notice by the stockholder to be timely must be so received not later than the later of the close of business 90 days prior to such annual meeting or the 10th day following the day on which such notice of the date of the annual meeting was mailed or such public disclosure of the date of the annual meeting was made.

ANNUAL REPORT

A copy of our Annual Report on Form 10-Kfor the fiscal year ended December 31, 2024, which includes financial statements, is being furnished with this proxy statement.

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HOUSEHOLDING OF PROXY MATERIALS

The SEC has adopted rules that permit companies and intermediaries (e.g., brokers) to satisfy the delivery requirements for the Notice of Internet Availability of Proxy Materials and proxy materials with respect to two or more stockholders sharing the same address by delivering a single Notice of Internet Availability of Proxy Materials addressed to those stockholders. This process, which is commonly referred to as "householding," potentially means extra convenience for stockholders and cost savings for companies.

The Company expects that many brokers with account holders who are the Company's stockholders will be "householding" the Company's proxy materials. A single Notice of Internet Availability of Proxy Materials or proxy materials will be delivered to multiple stockholders sharing an address unless contrary instructions have been received from the affected stockholders. If you have received notice from your broker that it will be "householding" communications to your address, "householding" will continue until you are notified otherwise or until you revoke your consent. We will promptly deliver a separate copy of these documents to you upon written or oral request to our Investor Relations Department by mail at Sixth Street Specialty Lending, Inc., 888 7th Avenue, 41st Floor, New York, NY 10106, Attention: TSLX Investor Relations, by email at [email protected] or by phone at 469-621-2033.If, at any time, you no longer wish to participate in "householding" and would prefer to receive a separate proxy statement, annual report and/or Notice of Internet Availability of Proxy Materials, please notify your broker. Stockholders who currently receive multiple copies of the proxy statement, annual report and/or Notice of Internet Availability of Proxy Materials at their addresses and would like to request "householding" of their communications should contact their brokers.

WHETHER OR NOT YOU PLAN TO ATTEND THE MEETING, WE URGE YOU TO VOTE OVER THE INTERNET, BY PHONE, OR BY MARKING, SIGNING AND RETURNING YOUR PROXY OR VOTING INSTRUCTION CARD AS SOON AS POSSIBLE. NO POSTAGE IS NECESSARY IF MAILED IN THE UNITED STATES.

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PRIVACY PRINCIPLES

The Company is committed to maintaining the confidentiality, integrity and security of nonpublic personal information relating to investors. The following information is provided to help you understand what personal information the Company collects, how it protects that information and why, in certain cases, it may share information with select other parties.

The Company may collect nonpublic personal information regarding investors from sources such as subscription agreements, investor questionnaires and other forms; individual investors' account histories; and correspondence between the Company and individual investors. The Company may share information that it collects regarding an investor with its affiliates and the employees of such affiliates for legitimate business purposes, for example, in order to service the investor's accounts or provide the investor with information about other products and services offered by the Company or its affiliates that may be of interest to the investor. In addition, the Company may disclose information that it collects regarding investors to third parties who are not affiliated with the Company (i) as authorized by investors in investor subscription agreements or the Company's organizational documents, (ii) as required by law or in connection with regulatory or law enforcement inquiries, or (iii) as otherwise permitted by law to the extent necessary to effect, administer or enforce investor or Company transactions.

Any party that receives nonpublic personal information relating to investors from the Company is permitted to use the information only for legitimate business purposes or as otherwise required or permitted by applicable law or regulation. In this regard, for officers, employees and agents of the Company and its affiliates, access to such information is restricted to those who need such access to provide services to the Company and investors. The Company maintains physical, electronic and procedural safeguards to seek to guard investor nonpublic personal information. Third parties that handle this information shall agree to follow the standards the Company has established. All safeguards apply to nonpublic personal information of current, former and prospective investors.

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SCAN TO VIEW MATERIALS & VOTE VOTE BY INTERNET-www.proxyvote.com or scan the QR Barcode above SIXTH STREET SPECIALTY LENDING, INC. Use the Internet to transmit your voting instructions and for electronic delivery of 2100 MCKINNEY AVENUE, SUITE 1500 information. Vote by 11:59 P.M. ET on 05/21/2025. Have your proxy card in hand when DALLAS, TX 75201 you access the web site and follow the instructions to obtain your records and to create an electronic voting instruction form. ELECTRONIC DELIVERY OF FUTURE PROXY MATERIALS If you would like to reduce the costs incurred by our company in mailing proxy materials, you can consent to receiving all future proxy statements, proxy cards and annual reports electronically via e-mailor the Internet. To sign up for electronic delivery, please follow the instructions above to vote using the Internet and, when prompted, indicate that you agree to receive or access proxy materials electronically in future years. VOTE BY PHONE-1-800-690-6903Use any touch-tone telephone to transmit your voting instructions. Vote by 11:59 P.M. ET on 05/21/2025. Have your proxy card in hand when you call and then follow the instructions. VOTE BY MAIL Mark, sign and date your proxy card and retuit in the postage-paid envelope we have provided or retuit to Vote Processing, c/o Broadridge, 51 Mercedes Way, Edgewood, NY 11717. TO VOTE, MARK BLOCKS BELOW IN BLUE OR BLACK INK AS FOLLOWS: KEEP THIS PORTION FOR YOUR RECORDS DETACH AND RETURN THIS PORTION ONLY THIS PROXY CARD IS VALID ONLY WHEN SIGNED AND DATED. For Withhold For All To withhold authority to vote for any All All Except individual nominee(s), mark "For All Except" and write the number(s) of the The Board of Directors recommends you vote FOR the following: nominee(s) on the line below. 0 0 0 1. Election of Directors Nominees 01) P. Emery Covington 02) Jennifer Gordon 03) Judy Slotkin The Board of Directors recommends you vote FOR the following proposal: For Against Abstain 2. To ratify the selection of KPMG LLP as the Company's independent registered public accounting firm for the 0 0 0 fiscal year ending December 31, 2025. NOTE: The named proxies are also authorized to transact such other business as may properly come before the 2025 Annual Meeting of Stockholders or any postponement or adjournment thereof. . 2 . 0 . 0 R1 1 _ Please sign exactly as your name(s) appear(s) hereon. When signing as attorney, executor, administrator, or other fiduciary, please give full title as such. Joint owners should each sign personally. All holders must sign. If a corporation or partnership, please sign in full corporate or 0000661203 partnership name by authorized officer. Signature [PLEASE SIGN WITHIN BOX] Date Signature (Joint Owners) Date

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting: The Notice and Proxy Statement and Form 10-Kare available at www.proxyvote.com SIXTH STREET SPECIALTY LENDING, INC. Annual Meeting of Stockholders May 22, 2025 9:30 AM EDT This proxy is solicited by the Board of Directors The stockholders hereby appoints Ian Simmonds and Anton Brett, or either of them, as proxies, each with the power to appoint his/her substitute, and hereby authorizes them to represent and to vote, as designated on the reverse side of this ballot, all of the shares of common stock of SIXTH STREET SPECIALTY LENDING, INC. that the stockholders are entitled to vote at the Annual Meeting of Stockholders to be held at The Offices of Simpson Thacher & Bartlett LLP, located at 425 Lexington Avenue, 30th Floor New York, NY 10017, at 9:30 AM EDT on May 22, 2025 and any adjournment or postponement thereof. This proxy, when properly executed, will be voted in the manner directed herein. If no such direction is made, this proxy will be voted in accordance with the Board of Directors' recommendations. . 2 . 0 . 0 R1 _ 2 0000661203 Continued and to be signed on reverse side